Bald Spot on Leg

I just recently got a new chinchilla as a playmate for a chinchilla I already have (No worries they're slowly being integrated and they're never by themselves without supervision) however I've noticed that there is a bald spot on the newer chinchillas wrist area and I looked online and thought maybe it was dry skin so I put on some lotion that is super safe for even babies to eat it (again don't worry I made sure it was gooped on their in case he is allergic to it) but as I was doing this I noticed that the entire leg all the way to the sternum is pretty much bald.

No where else is being bitten and my other chinchilla is not experiencing anything like this either so would it be fungus if it's not spreading? I'm a microbiology major in college and I would assume fungus would spread quickly and over the two chinchillas.